The process as described in the aforementioned copending parent application Ser. No. 508,848 is directed to a vacuum dissociation of a pelletized molybdenite concentrated feed material at an elevated temperature enabling recovery of the volatilized sulfur as a valuable by-product and employing a terminal hydrogen sweep treatment to remove the residual sulfur, thereby producing pellets of relatively pure metallic molybdenum. The present continuation-in-part application is directed to the further embodiment of producing ferromolybdenum alloys containing controlled amounts of iron and molybdenum which are eminently suitable for use as an alloying addition agent in steelmaking operations and the like.
Ferromolybdenum alloys are produced in accordance with prior art practices by either employing a thermit process or an electric furnace reduction process. Both of these techniques require substantial amounts of labor and energy and are, therefore, somewhat costly. In the thermit process, for example, a molybdenum oxide feed material derived from the roasting of a molybdenite (MoS.sub.2) concentrate is mixed with reducing agents, such as silicon and aluminum, which through an exothermic thermit-type reaction produces an ingot or button of the alloy which is usually of a segregated structure and further requires crushing and sizing prior to shipment and use. The slag produced, for economic reasons, is usually subjected to further treatment for recovery of residual metal values and the treated residue is discarded. In addition to the relatively high costs of the reducing agents required in the thermit process, further problems are presented from an environmental standpoint as a result of the disposal of the slag produced and the treatment required of the gases evolved during the exothermic reaction.
The present process overcomes many of the problems and disadvantages associated with prior art techniques for producing ferromolybdenum alloys by utilizing a molybdenite concentrate directly as the starting material without requiring a roasting treatment to convert the feed to the oxide state. Carbon is employed as a low cost reducing agent, eliminating the formation of any slag, whereby a ferromolybdenum alloy is obtained which is of a nonsegregated structure and sulfur and other constituents evolved during the vacuum smelting operation can be recovered as valuable by-products.